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EpidemiologyEpidemiology

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IntroductionIntroduction

• The term epidemiology is derived from the The term epidemiology is derived from the Greek word epidemic. Greek word epidemic. – Epi means-Among, upon, Epi means-Among, upon, – Demos means study population or people and Demos means study population or people and – Logos means scientific study.Logos means scientific study.

• SoSo– it is the scientific study of the disease pattern in it is the scientific study of the disease pattern in

human population. human population. – In broad sense, it is the study of effects of multiple In broad sense, it is the study of effects of multiple

factors on human health. factors on human health. – It is multidisciplinary subject involving those of It is multidisciplinary subject involving those of

the physician, Biologists, Public Health experts, the physician, Biologists, Public Health experts, Health educators etc.Health educators etc.

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DefinitionsDefinitions

• The science of infective diseases, their The science of infective diseases, their prime causes, propagation and prime causes, propagation and prevention. (Stallbrass 1931.)prevention. (Stallbrass 1931.)

• The science of the mass phenomena of The science of the mass phenomena of infectious diseases or the natural history infectious diseases or the natural history of infectious diseases. (Frost 1927)of infectious diseases. (Frost 1927)

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DefinitionsDefinitions

• The study of the disease, any diseases, as The study of the disease, any diseases, as a mass phenomenon. (Greenwood 1935)a mass phenomenon. (Greenwood 1935)

• The study of condition known or The study of condition known or reasonably supposed to influence the reasonably supposed to influence the prevalence of disease. (Lumsden 1936)prevalence of disease. (Lumsden 1936)

• Epidemiology as, study of the distribution Epidemiology as, study of the distribution and determinants of diseases frequency in and determinants of diseases frequency in man. (Mac Mohan and Pugh)man. (Mac Mohan and Pugh)

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The widely accepted definition The widely accepted definition of epidemiology is,of epidemiology is,

• ""The study of the distribution and The study of the distribution and determinants of health related states determinants of health related states or events in specified population and or events in specified population and the application of the study to the application of the study to control of health problems“control of health problems“

(J.M. Last 1988)(J.M. Last 1988)

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Basic Tenets of Basic Tenets of epidemiologyepidemiology

• Target of a study in epidemiology is human Target of a study in epidemiology is human Population as Geographical area, Age, Sex, Population as Geographical area, Age, Sex, Ethnicity, Race etc.: the most common population in Ethnicity, Race etc.: the most common population in epidemiology is the population is a given area or epidemiology is the population is a given area or country at a given time. Since the structure of country at a given time. Since the structure of population varies at each time such variations also population varies at each time such variations also have to be taken in to consideration during data have to be taken in to consideration during data analysis. analysis.

• All findings must relate to the defined population. All findings must relate to the defined population. Enumeration is not enough in epidemiology, the Enumeration is not enough in epidemiology, the population at risk of developing that diseases need population at risk of developing that diseases need to be enumerated as well.to be enumerated as well.

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Basic Tenets of Basic Tenets of epidemiologyepidemiology

• Conclusions are based of comparisons: Conclusions are based of comparisons: comparing the rates of diseases frequency comparing the rates of diseases frequency among the exposed and unexposed and the among the exposed and unexposed and the unexposed is an important epidemiological unexposed is an important epidemiological method.method.

• Description of events by time, place and person. Description of events by time, place and person. Getting answer for when, where and who are Getting answer for when, where and who are affected is very important in epidemiology to affected is very important in epidemiology to formulate hypothesis about its causation. Other formulate hypothesis about its causation. Other important aspects are what, why and how of the important aspects are what, why and how of the events. events.

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Aims of EpidemiologyAims of Epidemiology

According to the International Epidemiological According to the International Epidemiological Association (IEA) Epidemiology has three main aims.Association (IEA) Epidemiology has three main aims.

– To describe and analyze diseases occurrence and To describe and analyze diseases occurrence and distribution in human populations;distribution in human populations;

– To identify etiological factors in the pathogenesis of To identify etiological factors in the pathogenesis of diseases;diseases;

– To provide the data essential to the planning, To provide the data essential to the planning, implementation and evaluation of services for the implementation and evaluation of services for the prevention, control and treatment of diseases and to the prevention, control and treatment of diseases and to the setting up of priorities among those services.setting up of priorities among those services.

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The ultimate aims of epidemiology can The ultimate aims of epidemiology can be concluded in to two followings be concluded in to two followings

points.points.

• To eliminate or reduce the health To eliminate or reduce the health problem or its consequences andproblem or its consequences and

• To promote the health and wellbeing To promote the health and wellbeing of society as a whole.of society as a whole.

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Uses of epidemiologyUses of epidemiology

• Investigation of causation of disease.Investigation of causation of disease.

Genetic FactorsGenetic Factors

Good HealthGood Health Ill Health Ill Health

Environmental FactorsEnvironmental Factors

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Uses of epidemiologyUses of epidemiology

• Study of the natural history and Study of the natural history and prognosis of diseases.prognosis of diseases.

Good health Good health Sub clinical ChangesSub clinical Changes

Clinical DiseasesClinical Diseases

DeathDeath

RecoveryRecovery

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Uses of epidemiologyUses of epidemiology

• Description of the health status of the Description of the health status of the populations. It includes proportion with populations. It includes proportion with ill Health, change over time, change ill Health, change over time, change with age etc.with age etc.

• Evaluation of the interventions.Evaluation of the interventions.

• Planning health services, Public policy Planning health services, Public policy and programs.and programs.

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And, RecentlyAnd, Recently

• epidemiologists have become involved in epidemiologists have become involved in evaluation the effectiveness and efficacy evaluation the effectiveness and efficacy of health services, by determining the of health services, by determining the appropriate length of stay in hospital for appropriate length of stay in hospital for specific conditions, the value of treating specific conditions, the value of treating High blood pressure, the efficiency of High blood pressure, the efficiency of sanitation measures to control diarrhoeal sanitation measures to control diarrhoeal diseases, the impact on public health of diseases, the impact on public health of reducing lead activities in petrol etc.reducing lead activities in petrol etc.

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Components of Components of epidemiologyepidemiology

Disease frequency: -Disease frequency: - • The core characteristics of epidemiology are to The core characteristics of epidemiology are to

measure the frequency of diseases, disability or measure the frequency of diseases, disability or death in a specified population. it is always as death in a specified population. it is always as the rate, ratio and proportion. the rate, ratio and proportion.

• Much of the subject of epidemiology subject Much of the subject of epidemiology subject matter of measurement of diseases and health matter of measurement of diseases and health related events falls in the domain of biostatistics, related events falls in the domain of biostatistics, which is a basic tool of epidemiology. This helps which is a basic tool of epidemiology. This helps to development of strategies for prevention or to development of strategies for prevention or control of health related problems.control of health related problems.

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Components of Components of epidemiologyepidemiologyDistribution of diseases: -Distribution of diseases: - • Health events occur in pattern in community and Health events occur in pattern in community and

this pattern varies from community to community. this pattern varies from community to community. • Also health events or diseases condition affect Also health events or diseases condition affect

population at various age groups, different sexes, population at various age groups, different sexes, different subgroups of population. different subgroups of population.

• Distributions of events are based on time, place, Distributions of events are based on time, place, and person. We can analyze whether any increases and person. We can analyze whether any increases or decreases occur for a particular condition. or decreases occur for a particular condition. Epidemiology addresses itself to a study of these Epidemiology addresses itself to a study of these variations or patterns, which may suggest or lead variations or patterns, which may suggest or lead to measure to control or prevent the diseases. An to measure to control or prevent the diseases. An important outcome of this study is formulation of important outcome of this study is formulation of etiological hypothesis. etiological hypothesis.

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Components of Components of epidemiologyepidemiology

Determinants of diseases;Determinants of diseases;- - • Epidemiology helps in identifying the Epidemiology helps in identifying the

causative agent or the risk/predisposing causative agent or the risk/predisposing factors of diseases .factors of diseases .

• This is one of the real uses of This is one of the real uses of epidemiology. Understanding the factors epidemiology. Understanding the factors leading to any programs for the control leading to any programs for the control of those diseases. of those diseases.

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History of epidemiologyHistory of epidemiology• The history of epidemiology has its origin in the The history of epidemiology has its origin in the

idea, goes back to (400BC) Hippocrates through idea, goes back to (400BC) Hippocrates through John Graunt (1662), William Farr, John Snow and John Graunt (1662), William Farr, John Snow and others that environmental factors can influences others that environmental factors can influences the occurrences of diseases in stead of the occurrences of diseases in stead of supernatural viewpoint of diseases. supernatural viewpoint of diseases.

• John Graunt analysis and published the mortality John Graunt analysis and published the mortality data in 1662.He was the first quantify pattern of data in 1662.He was the first quantify pattern of death, birth and diseases occurances.death, birth and diseases occurances.

• No one built upon Graunt’s work until No one built upon Graunt’s work until 1800’s.when William Farr began to systematically 1800’s.when William Farr began to systematically collect and analyst the Britain’s mortality collect and analyst the Britain’s mortality statistics. Farr considered as the father of vital statistics. Farr considered as the father of vital statistics and diseases classifications.statistics and diseases classifications.

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History of epidemiologyHistory of epidemiology

• Meanwhile John Snow was conducting the series of Meanwhile John Snow was conducting the series of investigations in London that later earned him the title investigations in London that later earned him the title father of field epidemiology. Snow conducted his father of field epidemiology. Snow conducted his classical study in 1854 when an epidemic of cholera classical study in 1854 when an epidemic of cholera developed in the golden square of London. During the developed in the golden square of London. During the time of microscope development, snow conducted time of microscope development, snow conducted studies of cholera outbreak both to discover the causes studies of cholera outbreak both to discover the causes of diseases and prevent its recurrences. of diseases and prevent its recurrences.

• During that time two men (Farr and snow) had major During that time two men (Farr and snow) had major disagreement about the cause of cholera. Farr adhere disagreement about the cause of cholera. Farr adhere to what was the called miasmatic theory of diseases, to what was the called miasmatic theory of diseases, according to this theory which was commonly held at a according to this theory which was commonly held at a time diseases was transmitted by a miasma or cloud time diseases was transmitted by a miasma or cloud that clung low on the earth surface. that clung low on the earth surface.

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History of epidemiologyHistory of epidemiology

• However Snow did not agree he believed that However Snow did not agree he believed that cholera is transmitted through contaminated cholera is transmitted through contaminated water. He began his investigation by water. He began his investigation by determining where in this area person with determining where in this area person with cholera lived and worked. He then used this cholera lived and worked. He then used this information to map for distribution of information to map for distribution of diseases. Snow believed that water was the diseases. Snow believed that water was the source of infection for cholera. He marked the source of infection for cholera. He marked the location and searches the relationship location and searches the relationship between cases and water sources. He found between cases and water sources. He found that cholera was transmitted though that cholera was transmitted though contaminated water. This was the major contaminated water. This was the major achievement in epidemiology. achievement in epidemiology.

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History of epidemiologyHistory of epidemiology

• In the 1900s epidemiologists extend their methods In the 1900s epidemiologists extend their methods to noninfectious diseases and studied effect of to noninfectious diseases and studied effect of behaviors and life style in human health. There are behaviors and life style in human health. There are some important achievements in epidemiology they some important achievements in epidemiology they are; are; – John Snow and cholera epidemic in London in 1848-1854.John Snow and cholera epidemic in London in 1848-1854.– Framingham heart study started in 1950 in Massachusetts, Framingham heart study started in 1950 in Massachusetts,

USA and still continuing to identify the factors leading to USA and still continuing to identify the factors leading to the development of the coronary heart diseases.the development of the coronary heart diseases.

– Smoking and lung cancer by Doll and Hill in 1964.Smoking and lung cancer by Doll and Hill in 1964.– Polio Salk vaccine field trial in 1954 to study the protective Polio Salk vaccine field trial in 1954 to study the protective

efficacy of vaccine in a million school children. efficacy of vaccine in a million school children. – Methyl Mercury poisoning 1950s In Minamata Methyl Mercury poisoning 1950s In Minamata

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Field of epidemiologyField of epidemiology

Epidemiology covers the various types of field Epidemiology covers the various types of field in different types of activities. It is applied in different types of activities. It is applied in every field as agricultural, economics, in every field as agricultural, economics, statistics etc. They are asstatistics etc. They are as

• Clinical epidemiologyClinical epidemiology• Geographical epidemiologyGeographical epidemiology• Social epidemiologySocial epidemiology• Statistical epidemiologyStatistical epidemiology• Descriptive epidemiologyDescriptive epidemiology• Analytical epidemiologyAnalytical epidemiology• Experimental epidemiologyExperimental epidemiology• Infectious diseases epidemiology etc.Infectious diseases epidemiology etc.

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Comparison between Clinical medicine and Epidemiology

S.N.

Area Epidemiology Clinical Medicine

1 Unit of study Population ( Defined or at risk) Cases or case

2 objectives To identify the source, Mode of transmission, etiological factors,

To cure the patient.

3 Examination Group of people or community Individual case

4 Concern with Sick and healthy Sick

5 Diagnosis By survey, research Individual test done.

6 Where to go? Experts goes to community Patient goes to hospital

7 Area concern Mainly concern to preventive and promotive through intervention

Mainly in curative field

8 Concept Bio-statistical Bio-medical

9 Presentation of result

By tables, charts and diagrams By laboratory and others reports

10 Time Long process Short time sometimes long time

11 outcome Planning, implementation and health promotion

Cured or disability or death

Concept of disease Concept of disease causation causation

• Germ theory of diseasesGerm theory of diseases

• Epidemiological triadsEpidemiological triads

• Multifactorial causationMultifactorial causation

• Web of causationWeb of causation

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Epidemiological triadsEpidemiological triads

• Agent -Agent -Biological, chemical, physical, nutritional, SocialBiological, chemical, physical, nutritional, Social

• Host factor- Host factor- Age, sex, heredity, nutrition, Occupation, Age, sex, heredity, nutrition, Occupation, Custom, habits, Immunity power, Biological-Blood sugar, Custom, habits, Immunity power, Biological-Blood sugar, Cholesterol, Housing, Marital status, socio-economic statusCholesterol, Housing, Marital status, socio-economic status

• Environmental Factor- Environmental Factor- Physical, Biological, PsychosocialPhysical, Biological, Psychosocial

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Example – Typhoid FeverExample – Typhoid Fever

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Disease

Example – Cervical cancerExample – Cervical cancer

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Disease

Dynamic of diseases Dynamic of diseases TransmissionTransmission

• Source of Infection or reservoir of Source of Infection or reservoir of infectioninfection

• Mode of transmissionMode of transmission

• Susceptible HostSusceptible Host

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Reservoir of infectionReservoir of infection

• Human reservoirHuman reservoir•Case – Case – Clinical, Sub clinical, LatentClinical, Sub clinical, Latent

•Carrier- Carrier- Incubatory, Convalescent, HealthyIncubatory, Convalescent, Healthy

• Animal Reservoir – Animal Reservoir – ZoonoticZoonotic

• Reservoir of nonReservoir of non- - living Things- Soilliving Things- Soil

• Source of Infection- Secretion/ Excretion of reservoirs, Some times Source of Infection- Secretion/ Excretion of reservoirs, Some times ReservoirsReservoirs

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Mode of Diseases Mode of Diseases transmissiontransmission• DirectDirect

• Direct ContactDirect Contact

• Droplet InfectionDroplet Infection

• Inoculation in to skin Inoculation in to skin or mucosaor mucosa

• Contact with Contact with infected Soilinfected Soil

• VerticalVertical

• IndirectIndirect• Vehicle borne Vehicle borne

diseasedisease

• Vector Borne diseaseVector Borne disease– BiologicalBiological– MechanicalMechanical

• Air Borne DiseaseAir Borne Disease– Droplet NucleiDroplet Nuclei– Infective DustInfective Dust

• FomiteFomite

• FingersFingers

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Susceptible HostSusceptible Host

Low immunity person. High risk personLow immunity person. High risk person

• Portal of entryPortal of entry Mode of TransmissionMode of Transmission

• Suitable PlacesSuitable Places

• Develop/ Multiplication/Disease/CarrierDevelop/ Multiplication/Disease/Carrier

• Portal of exitPortal of exit• RespiratoryRespiratory

• GastrointestinalGastrointestinal

• UrinaryUrinary

• SkinSkin

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Diseases prevention and controlDiseases prevention and control

• Prevention of source or reservoirPrevention of source or reservoir• Early diagnosisEarly diagnosis

• NotificationNotification

• Epidemiological InvestigationEpidemiological Investigation

• IsolationIsolation

• TreatmentTreatment

• QuarantineQuarantine

• Interruption of the disease transmissionInterruption of the disease transmission

• Prevention of susceptible hostPrevention of susceptible host• ImmunizationImmunization

• Health educationHealth education

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Epidemiological Epidemiological InvestigationInvestigation• Verification of diagnosisVerification of diagnosis

• Confirmation of the existence of an epidemicConfirmation of the existence of an epidemic

• Defining the population at riskDefining the population at risk• Obtaining the map of the areaObtaining the map of the area

• Counting the populationCounting the population

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ContinueContinue

• Rapid search for all cases and their characteristicsRapid search for all cases and their characteristics• Medical SurveyMedical Survey

• Epidemiological case sheetEpidemiological case sheet

• Searching for more casesSearching for more cases

• Data analysisData analysis• Time Time

• PlacePlace

• PersonPerson  

• Formulation of hypothesisFormulation of hypothesis

• Testing of hypothesis Testing of hypothesis 

• Evaluation of ecological factors Evaluation of ecological factors 

• Further investigation of population at risk Further investigation of population at risk 

• Writing the reportWriting the report

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study design in study design in EpidemiologyEpidemiology

• Observational StudyObservational Study– Descriptive studiesDescriptive studies– Analytical StudiesAnalytical Studies

• Ecological Study: - Correlation Study unit is a population.Ecological Study: - Correlation Study unit is a population.

• Cross-Sectional Study: - prevalent Study Individual is a unit of study.Cross-Sectional Study: - prevalent Study Individual is a unit of study.

• Case-Control Study: - case-reference with individual is a unit of study.Case-Control Study: - case-reference with individual is a unit of study.

• Cohort study:-Follow up study with individual is a unit of study.Cohort study:-Follow up study with individual is a unit of study.

  

• Experimental StudiesExperimental Studies– Randomized Control TrialsRandomized Control Trials– Field TrialsField Trials– Community TrialsCommunity Trials

  

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